1. Field of the Invention
This invention relates to an applanation tonometer for providing a measurement of the intraocular fluid pressure inside the eye of a patient undergoing testing. The applanation tonometer includes cornea alignment means by which the patient is able to advise a vision professional when a light source of the tonometer is properly aligned with his cornea so that intraocular fluid pressure can be accurately measured while dwell time on the cornea and patient discomfort can be minimized.
2. Background Art
A tonometer is a non-invasive instrument which is used to measure pressure or tension in human or veterinary tissues. In the human body, intraocular fluid pressure in the eye (IOP) is measured to provide basic information for the diagnosis and treatment of glaucoma and related eye disease. Ease of application, accuracy of measurement and precise alignment of the tonometer between a (e.g., laser) light source and the patient's cornea are of paramount importance to obtaining reliable IOP measurements.
One example of an applanation tonometer that is adapted to make accurate IOP measurements is described in Patent Application Publication No. US 2012/0108941 published May 3, 2012. This applanation tonometer has a prism assembly at one end thereof, a light source module at the opposite end, and an intermediate beam splitter module located therebetween. The prism assembly includes a piezo element located adjacent a conical prism that tapers to a contact tip to be pressed against the patient's cornea to achieve applanation during the measurement of IOP. The light source module includes a laser or LED that supplies incoming light to the prism assembly to illuminate the patient's cornea. The beam splitter module includes a photo detector and an internal reflective surface that is aligned to reflect to the photo detector light which is reflected outwardly through the prism assembly before, during and after full applanation. The outputs of the piezo element and the photo detector provide force and area data pairs which are processed to provide a measurement of IOP.
It would be desirable to enhance the accuracy of the IOP measurements and minimize the time during which the measurements are made by being able to quickly and easily align the tonometer with respect to the patient's cornea, especially in cases where the patient moves his eye. To accomplish the foregoing, what would be advantageous is an alignment tool for use with the applanation tonometer by which to enable the patient to determine when the light source module and the prism module of the tonometer are ideally aligned with respect to his cornea so that the tonometer can be moved towards and into contact therewith.